A hallmark of cancer is uncontrolled cell division, and many cancers therapeutic measures work by disrupting microtubule dynamics and/or mitotic spindle architecture to arrest cell division. It is clear that proper microtubule organization and length regulation are important for the successful completion of cell division. In this study, we will focus on mechanisms for how microtubule-associated proteins regulate microtubule lengths and organize spindle microtubules during mitosis. To provide a basis for these and future studies, we will first focus on microtubule dynamics in the absence of regulating proteins to better understand the relationship between microtubule tip structures and microtubule dynamics. Our preliminary modeling results predict that microtubule tip structures are important for self-regulating microtubule dynamics. We will investigate this hypothesis using in-vitro fluorescence and electron microscopy, as well as in-vivo analysis in budding yeast. Then, we will investigate the mechanism for tip-tracking of important microtubule plus end-binding proteins, such as Eb1, to determine whether the microtubule tip structures could provide a platform for targeting of important length-regulating proteins to the microtubule tip. Finally, we will investigate the role of microtubule- associated proteins in organizing microtubules into a mitotic spindle during cell division. Specifically, we will use in-vivo experiments in budding yeas cells, in-vitro reconstitution, and computer simulations to determine the role and mechanism of Kinesin-14 minus-end directed motors in establishing proper microtubule bundling in mitotic spindles.